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Estimation of TOPEX/POSEIDON sea level baroclinic contribution using the results of an OGCM simulation vertical mode decomposition

Boris Dewitte and Gilles Reverdin

We investigate how much information on subsurface variability in the equatorial Pacific can be estimated from TOPEX/POSEIDON sea level data. For this, we first investigate the vertical structure of the variability in the equatorial Pacific in an 1985-1994 simulation of an Ocean General Circulation Model. Linear vertical modes are estimated at each grid point and time step of the OGCM simulation. Contribution of baroclinic modes to surface zonal current and sea level anomalies are derived. We find comparable contribution of the first two modes with different spatial distribution in the equatorial wave guide. Third and fourth moeds exhibit varaiability peaks in the east and in the westernmost part of the basin. Higher-order modes variability is concentrated near the dateline close to the location of the maximum in zonal wind stress variability.
An E-EOF (Extended EOF) analysis is used to derive the statistically dominant horizontal mode for each baroclinic mode in the OGCM. TOPEX data are then projected onto the E-EOF spatial structures to derive an estimation of TOPEX sea level baroclinic contributions. Decomposing the results into Kelvin and Rossby modes allows to reconstruct the associated baroclinic zonal current anomalies. We compare the results with the one of multi-mode linear simulations with the projection coefficients and phase speeds derived from the OGCM simulatino at various latitude.


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